A process for the production of pourable and free flowing granules of materials or mixtures thereof which are suitable for use as wetting agents, detergents or cleaning products wherein an aqueous solution or suspension of the wetting agents, detergents or cleaning products is dried using a hot gas stream of superheated steam. Drying is terminated before the granules are damaged by heat, and the hot gas stream is freed from entrained particles of the materials by means of filters.

1. Field of the Invention
This invention relates to a process for the production, more particularly the continuous production, of pourable and free flowing granules of useful materials or mixtures of useful materials, which are suitable for use as and/or in wetting agents, detergents and/or cleaning products, from aqueous solutions and/or suspensions by spray drying or fluidized bed spray granulation or the like in a drying vessel using a hot gas stream. The process according to the invention involves one or more drying steps, superheated steam being used as the drying gas.
The spray drying of aqueous preparations of useful materials of the type mentioned, which are widely used, for example, as laundry detergents, has been carried out on an industrial scale for decades. Hot air or mixtures of air and hot waste combustion gases are used as the drying gas stream. Washing powders or useful materials and/or mixtures of useful materials for the production of laundry detergents in pourable and free-flowing powder form are produced in corresponding spray drying towers, generally at ambient pressure, either in co-current or more often in countercurrent.
In their application DE-A 40 30 688, applicants describe a process for the production of solid, fine-particle pourable and free-flowing useful materials or mixtures thereof for wetting agents, detergents and/or cleaning products from aqueous preparations thereof, superheated steam being used as the drying hot gas stream and drying of the particulate material being terminated before it is endangered by heat. If necessary, the long-term pourability and free-flow of the material thus partly dried is ensured by addition of mixture constituents which are capable of binding limited quantities of water. In addition to or instead of this measure, the particulate material may also be aftertreated to homogenize its residual moisture content and/or after-dried under conditions which do not affect the useful material. The teaching of the invention described hereinafter is concerned with a specific embodiment of this process according to the earlier application cited above. The teaching according to the invention seeks to enable high-quality useful materials or mixtures of useful materials of the type in question to be obtained where superheated steam is used as the drying gas. The problem addressed by the present invention will become clear from the following considerations presented purely by way of example:
The requirements which high-quality detergents, particularly laundry detergents, are now having to satisfy in practice are not confined to performance expectations. The visual appearance, for example a light color in the case of laundry detergents, and other physical properties, such as free flow, a high apparent density, rapid dissolution in water and good dispensing properties and the like, are also important requirements.
The problem addressed by the present invention was to provide optimized conditions for the application in question of drying useful materials with superheated steam as drying medium to enable the high-quality useful materials or mixtures of useful materials to be obtained in the dry state.
It is important in this connection to bear in mind the fact that practical experience in the application of drying processes using superheated steam as the drying gas has been very limited up till now although, basically, this technology has been known since the beginning of this century and has been repeatedly described in the literature. Earlier application DE-A 40 30 688 deals in detail with the relevant prior-art literature. Reference is made here to the corresponding observations in the earlier application and solely to the following publications which in turn cite numerous publications on this subject: A.M. Trommelen et al. "Evaporation and Drying of Drops in Super-heated Vapors" AIChE Journal 16 (1970) 857-867; Colin Beeby et al. "STEAM DRYING" Plenary Lecture, Pro. 4th Int. Drying Sym. Kyoto (eds. R. Toei and Arun S. Mujumdar) 1984, Vol. 1, 51-68 and W. A. Stein "Berechnung der Verdampfung von Fluussigkeit aus feuchten Produkten im Spruhturm (Calculating the Evaporation of Liquid from Moist Products in spray Drying Towers)", Verfahrenstechnik 7 (1973), 262-267.
Accordingly, the present invention relates to the solution to the problem stated above of obtaining high-quality useful materials or mixtures of useful materials which are suitable for use as and/or in wetting agents, detergents and/or cleaning products. More particularly, the present invention relates to a process for drying these water-containing valuable materials or mixtures of valuable materials, which may even be present as aqueous preparations, using superheated steam as the drying gas which is recycled to the drying stage after removal of the evaporated water.
Where superheated steam is used as the drying gas, the dust present in the recycled gas has to be removed to safeguard the operation of the circulation fan and the super-heater and to avoid deposits in the pipes. This applies in particular to a granulation process which includes spraying because the fine dust formed would lead to abrasion of the equipment arranged in the drying gas circuit.
Where drying is carried out with circulated super-heated steam, it is standard practice to remove the dust in cyclones (Drying 1980 (Volume I)--Developments in Drying, pages 320 to 331, more particularly FIG. 2, Hemisphere Publishing Corporation, New York (1980) and Gehrmann, Chem.-Ing.-Techn. 62 (1990) No. 10, pages A 512--A 520, more particularly FIG. 5). Where the materials to be dried are inorganic, the removal of dust in such cyclones is sufficient. However, where the material to be dried is organic, the filter dust present in the hot steam recycle gas tends to cake on the steam blower, the heat exchanger, the pipes and on other equipment. In this case, the cleaning effect of a cyclone is no longer sufficient.
2. Description of the Invention
According to the invention, therefore, the circulating steam is freed from entrained particles of the starting materials by means of filters consisting of woven fabrics and/or felts, preferably needle felt, more particularly tubular filters. In contrast to cleaning with cyclones, the dust content of the recycle gas can be reduced with filters to a value of 10 mg m.sup.3 and preferably to a value of 5 mg m.sup.3.
Where superheated steam is used as the drying gas, it cools down on flowing past the moist particles so that there is an increase in its water content. If the drying gas then flows through the filter, there is a danger of water condensing on the filter cloth or felt and in the clean gas zone which must definitely be avoided. For this reason, it is of advantage if the filters and/or the clean gas zone are additionally heated. The filter may be heated, for example, by a tube coil on the inner wall of the filter housing or by a heatable double jacket.
Where superheated steam is used as recycle gas for drying, filters have not hitherto been used for the removal of dust. On the one hand, drying with superheated steam necessitates higher temperatures at the dryer exit at which the filter material must not decompose. On the other hand, there is a danger of the filter medium hydrolyzing in the steam atmosphere. For these reasons among others, drying with superheated steam has hitherto been applied to materials also which do not form large amounts of dust so that cyclones are sufficient for dust removal. According to the invention, however, the filters used for removing dust from the drying gas must be resistant to hydrolysis, even at the high temperatures prevailing in the steam atmosphere, and must be temperature-resistant at the high exit temperatures of the drying gas.
To ensure that cleaning of the filters does not interfere with the drying process, the circulating steam is allowed to flow inwards through the tube filters which are exposed to surges of pressurized gas from inside, more particularly periodically, so that any particles of the starting material which have settled on the filters are removed. The brief surges of pressurized gas produce a pressure wave which travels over the entire surface of the tube. As a result, the filter tubes are stretched and the adhering fine dust is ejected downwards. In one advantageous embodiment, the cleaning sequence can be automatically controlled. To ensure that the steam atmosphere is not contaminated by foreign gases, for example air, and that inert conditions are maintained, superheated steam is advantageously used as the pressurized gas for cleaning the filters. Another advantage in this case is that the filter material does not have to be oxidation-resistant although an inert atmosphere is otherwise maintained.
Separate filter housings and additional units for discharging the filter dust from the housings are not necessary if the steam is made to circulate upwards in countercurrent to the material being dried and through the filters arranged in the upper part of the drying vessel. The fine dust removed accumulates directly in the drying vessel. In a particularly preferred embodiment, the steam is guided through filters arranged vertically above the spraying zone or the fluidized bed. In this case, the fine dust removed from the filter elements drops back into the spraying zone or the fluidized bed where it agglomerates with the other particles.
Another reason why the filter tubes are cleaned with steam is to rule out the danger of dust explosions. Product quality is also increased if oxygen is prevented from entering the recycle gas during the cleaning process.
In other embodiments, the invention relates to the use of this process for obtaining free-flowing surfactant solids, more particularly from the field of anionic surfactants based on natural materials, and also to its use for obtaining dried silicate-base useful materials which may be used in particular in laundry detergents and, finally, to the use of the described process for obtaining so-called laundry detergent tower powders to which temperature-sensitive and/or steam-volatile components may be subsequently added for the production of, or to complete the formulation of, the laundry detergents.
The technical teaching with which the present disclosure is concerned is a further development of earlier application DE-A 40 30 688 which has already been repeatedly cited. In the interests of completeness of disclosure of the present invention, the disclosure of that earlier application is hereby also specifically included as part of the disclosure of the present invention. In addition, the following process elements are important:
Under the working conditions according to the invention, drying with the superheated steam may also be carried out on the one hand as spray drying and/or on the other hand as fluidized bed drying. Starting materials of comparatively high water content are present, for example, as flowable and sprayable aqueous solutions, emulsions and/or suspensions of the useful materials or mixtures of useful materials to be dried. In one important embodiment, starting materials of this type are subjected to spray drying technology known per se. The spray drying process may be carried out in co-current or in countercurrent in correspondingly equipped spray drying towers. In general, the countercurrent principle is also preferably applied in the process according to the invention. If, on the other hand, the drying principle according to the invention is used in fluidized bed drying, the known working principles of possible particle enlargement may be applied in this case, too.
In general, the process according to the invention is carried out at normal pressure although the invention specifically includes moderate excess or reduced pressures.
In other respects, the process according to the invention may largely be carried out in accordance with applicants'earlier patent application cited at the beginning for drying the mixtures of useful materials in question with superheated steam as the drying gas. To complete the disclosure of the invention, the relevant passages of that earlier application are reproduced herein where necessary:
In the earlier application, the fact that optimal drying results by the action of hot steam in the end product of the process are not essential is regarded as crucial to understanding the teaching of the drying of mixtures of useful materials of the type in question with superheated steam. Basically, the same also applies to the teaching according to the invention. However, it has been found that, providing such troublesome factors as air or oxygen are reliably ruled out, even mixtures which, under conventional drying conditions with hot gases, tended to enter relatively quickly into unwanted reactions, for example discoloration, encrustation and the like, are comparatively immune to temperature. For drying with superheated steam, this means that safe operation both with superheated steam at comparatively high temperatures and degrees of drying to minimal residual moisture contents are possible without any adverse effect on the quality of the end product. Thus, residual moisture contents distinctly below 1% by weight, for example down to about 0.5% by weight or even lower, can be established in the dry material. At the same time, working temperatures of the used steam issuing from the drying zone above 100.degree. to 110.degree. C., preferably above 150.degree. C. and, more preferably, above 180.degree. C. can be applied.
Nevertheless, even fairly significant residual moisture contents can be tolerated providing the composition of the material ensures that the residual water is bound by a form of "internal drying" to such an extent that the long-term pourability and free flow of the dry material is guaranteed.
As described in the earlier application, the teaching of the invention also provides for after-treatment of the partly dried granules initially obtained in addition to or instead of this auxiliary measure. The aftertreatment may be carried out by two methods which may even be combined with one another.
The first of these methods is based on the fact that the individual degree of drying of the particular particle in question is determined by its particle size. If, in accordance with the invention, the drying process is terminated at a time when considerable quantities of residual moisture are still present in the material, integral consideration of the residual moisture content does only partial justice to reality. By differential consideration of the distribution of this residual moisture over the individual fractions of material, it has been found that the fine or ultrafine fractions can be dried very extensively or completely while the coarser fractions still contain such considerable quantities of moisture that the material removed from the spray drying zone is not guaranteed long-term pourability and free flow. In one important embodiment of the process according to the invention, therefore, "after-drying" of the primary material from the spray drying zone is achieved by an additional treatment step which--without exposing the powder-form material to the risk of developing tackiness--leads to homogenization of the moisture content over the material as a whole irrespective of the individual particle size. In this way, so much residual moisture can be introduced into the fine and ultrafine material from the still comparatively moist coarse particles of the material that, after this homogenization step, the long-term pourability and free flow of the dried material are guaranteed without further quantities of moisture having to be additionally eliminated from the bulk material.
This aftertreatment step may be carried out by any method which equalizes the moisture content of the individual particles and, at the same time, prevents them from adhering to one another. Circulation or shaking of the material initially obtained either continuously or discontinuously are mentioned as examples of such methods. Aftertreatment of the material in a fluidized bed having a very much higher solids density by comparison with spray drying can be particularly suitable. Any gases, for example quite simply ambient air, may be used for this purpose. Damage to the material by oxidation and/or unwanted contamination of the waste air is minimal or nonexistent and is easy to control. Since the material to be dried is removed from the spray drying zone at elevated temperature, typically of the order of 100.degree. C., a further slight reduction in the residual moisture content can be obtained by this subsequent homogenization of moisture in a fluidized bed, for example using ambient air.
However, in addition to or instead of this auxiliary measure, provision can also be made in the process according to the invention for a further reduction in the residual moisture content by additional drying. If after-drying proves to be desirable, one such additional after-drying step will generally be sufficient. However, after-drying in a sequence of several steps is not ruled out by the teaching of the invention. The after-drying step(s) is characterized in that it is carried out under conditions which do not significantly endanger the useful materials in the material to be dried. In principle, several process parameters are available for reducing that risk, including for example reducing the temperature of the hot gas phase, dispensing with superheated steam as the hot gas and replacing it with drying gases of different origin, for example air and/or inert gas, and changing over to another drying technology.
In one preferred embodiment of the process according to the invention, the solids density of the material to be dried in the hot gas stream is substantially increased where such an after-drying step is used, so that, in this after drying step, the process principles of fluidized bed drying follow spray drying from the first drying stage. This subsequent fluidized bed drying step may in turn be carried out with any drying gases. In the preferred embodiment of the invention, superheated steam is used as the hot gas in this step also. However, the intensive exchange of heat between the now comparatively closely packed solid particles can thus effectively counteract unwanted overheating of the material to be dried and, more particularly, the danger of overheating of the fine particles of that material. In preferred embodiments of the invention, it is again possible through the composition of the material to be dried to ensure that the elements of the "internal drying" discussed above can be used to bind any residual moisture still present.
Aqueous preparations of useful materials and combinations thereof from the field of wetting agents, detergents and/or cleaning products which are not damaged significantly if at all, by brief exposure to water or steam at a material temperature of 100.degree. to 110.degree. C. are particularly suitable for use in the process according to the invention. Components of this type which are not damaged by exposure to temperatures in the range mentioned for at least about 0.5 to 1 min. under the working conditions are particularly suitable useful materials. By controlling the process parameters--in addition to the design of the spray-drying zone, the working temperature range used in accordance with the invention and the droplet or particle size of the sprayed material are mentioned by way of example--it is possible to select residence times of a matter of seconds for the particular particles under the conditions of the superheated steam. It is crucial that the period of exposure to temperatures in this range can be kept so short in the process according to the invention that no substantial damage to the material to be dried occurs under the working conditions selected. For example, even surfactant compounds which are basically vulnerable to hydrolysis are largely undamaged by exposure to these working conditions for a few minutes. Thus, aqueous preparations of water-soluble and/or insoluble organic and/or inorganic useful materials from wetting agents, detergents and/or cleaning products which may be assigned, for example, to the following classes may be subjected to drying in the drying process according to the invention: surfactant or emulsifier components, inorganic and/or organic builders or builder components, washing alkalis, fillers or neutral salts, fabric softeners, bleach activators, auxiliaries for improving the soil suspending power of the liquors, such as redeposition inhibitors or even abrasives.
If it is necessary to retain considerable quantities of water in the product subjected to the main drying process and hence to bind this residual water to ensure the long-term pourability and free flow of the dried material, auxiliaries capable of fixing water, preferably in the form of particulate solids, are used in accordance with the invention. In this case, residual water may be fixed, for example, by binding as water of crystallization. However, limited quantities of water in solid particles of the type in question here can also be bound purely by absorption without causing any unwanted tackiness or adhesion of the particles to one another. The auxiliaries are at least used in quantities sufficient to guarantee pourability and stability in storage despite the residual moisture present in the material.
In one embodiment of the invention, the auxiliaries used to bind the residual water may be added to the dried fresh material, best immediately after it has been removed from the process, and intensively mixed therewith. In preferred embodiments, however, the auxiliaries binding the residual water are at least partly, preferably at least predominantly or, in general, completely added to the aqueous preparations of useful material before they are dried. This particular embodiment may always be applied when the particular temperature sensitivity of the material to be dried allows drying to be carried out to such an extent that the residual moisture remaining in the product can be adequately absorbed and bound by the auxiliaries used.
In one embodiment of the process according to the invention of particular advantage in this regard, corresponding useful materials from the field of wetting agents, detergents and/or cleaning products which themselves are sufficiently immune to temperature are used as the auxiliaries capable of binding residual water. Typical examples of such materials are inorganic materials capable of binding water of crystallization from the classes of builder components, washing alkalis and/or so-called fillers. Typical examples of the subclasses of useful materials listed here are silicate compounds capable of binding water of crystallization, more particularly from the class of zeolites. One example particularly characteristic of laundry detergents is detergent-quality zeolite NaA which has a calcium binding power of 100 to 200 mg CaO/g cf. DE 24 12 837). Typical examples of washing alkalis which bind water of crystallization are soda or sodium bicarbonate while sodium sulfate as neutral salt or filler has a pronounced capacity for binding considerable quantities of water of crystallization. However, in addition to or instead of the above-mentioned auxiliaries capable of binding water of crystallization, the residual water may also be bound by auxiliaries or corresponding useful materials capable of binding water by absorption. Thus, it is known that known starch- or cellulose-based redeposition inhibitors, fabric softeners, particularly those based on inorganic swellable silicates, and also a number of organic surfactant compounds which are solid under normal conditions are capable of absorbing considerable quantities of water without reacting by developing unwanted surface tackiness.
Depending on the temperature sensitivity of the useful materials or mixtures of useful materials used on the one hand and the nature and quantity of the auxiliaries used on the other hand, considerable residual water contents may remain in the dried material without endangering its long-term pourability and free flow. According to the invention, therefore, drying with superheated steam is terminated at residual water contents of the materials removed from the spray drying zone in the range from about 0.5 to 20% by weight, residual water contents in the range from about 5 to 12% by weight being preferred. The % by weight ranges mentioned relate to the weight of the fine-particle material removed from the steam zone. In another preferred embodiment of the invention, however, the amount of residual water which is not bound as water of crystallization is limited. Thus, it can be useful to limit this water content to at most about 10% by weight, preferably to no more than about 5 to 7% by weight and better still to values of at most about 1 to 3% by weight. Once again, the foregoing observations apply to the percentages by weight. Taking into account specialist knowledge of the field in question, the combination of desired properties is thus reliably achieved using superheated steam at high working temperatures: adequate drying at moderate temperatures, termination of the drying reaction even when considerable quantities of residual moisture are still present in the material, so that unwanted temperature effects are ruled out, and establishing long-term pourability and free flow in accordance with practical requirements.
As already mentioned, the process according to the invention offers additional possibilities for establishing the particular residual moisture content required which may be applied in addition to or instead of the principles of inner drying discussed in the foregoing. These alternative possibilities include the homogenization and/or step-by-step reduction of the moisture content of the material to be dried, the spray drying step being followed by one or more after drying steps which discharge troublesome quantities of moisture under comparatively moderate working conditions. Basically, any of the after drying techniques known to the expert in direct or indirect contact with hot gases are suitable for this purpose. In the preferred alternative of the process according to the invention, superheated steam is also used for after drying, best in an additional step. In order not to endanger the temperature-sensitive material, the temperature at which the superheated steam is used may be lower than in the spray drying stage. However, the following alternative has proved to be particularly successful:
The fine-particle material which still has an excessively high moisture content is removed from the spray drying zone and transferred to a following fluidized bed drying stage. Partial agglomeration of the still sufficiently moist material from the spray drying zone into a relatively coarse agglomerate is entirely acceptable or may even be desirable in a preferred embodiment of the teaching according to the invention. A partial agglomeration step may be used in particular to bind the fine component of the material removed from the spray drying zone and to combine it, for example, with the more moist coarse particles of the primary drying product. The following fluidized bed drying stage is carried out in known manner with the greatly increased solid densities in the drying zone which lead to the intensive exchange of heat between all the solid particles of the fluidized bed and, in this way, prevent unwanted increases in temperature in part of the granular material to be dried, even when steam which has been heated to comparatively high temperatures is again used as the drying gas.
In the after drying stage in the fluidized bed, limited quantities of residual moisture merely have to be removed to ensure the long-term free flow of the granular material, so that the residence time of the material in this fluidized bed aftertreatment can also be kept short, amounting for example to only a few minutes. Main drying in the spray drying zone and after drying in the fluidized bed may be carried out together in a continuous process or may even be carried out independently of one another as separate process steps. General specialist knowledge may be used in this regard.
In the second drying stage, the residual moisture still present may be partly or substantially completely removed. In practical embodiments, at least about 10 to 80% and preferably about 20 to 70% (based on the residual moisture) of the residual moisture present in the material removed from the spray drying zone is removed where this modification of the process is applied. Traces of moisture remaining in the material are rendered harmless by the internal drying.
In one important embodiment, the process according to the invention is used to dry mixtures of useful materials for the production of laundry detergents. The aqueous starting materials to be dried preferably contain washing-active surfactants together with builders and, optionally, washing alkalis and/or neutral salts. At least part of the multicomponent mixtures used is capable of binding and/or fixing residual water, more particularly in the form of water of crystallization. As in the spray drying of laundry detergents, the laundry detergent component of mixtures of the type in question is generally not exposed in its entirety to fluidized-bed spray granulation. This is precluded by the extreme temperature sensitivity of peroxide-containing bleach components, such as perborate monohydrate or tetrahydrate, and corresponding other particularly temperature-sensitive components. Enzymes, fragrances, bleach activators and other minor components are mentioned as further examples. Accordingly, the teaching of the present invention also provides inter alia for the production of so-called multicomponent tower powders which contain a large part of the components making up the final detergent in admixture with one another, but which are subsequently treated or mixed with other, liquid and/or solid active components. Known examples of such liquid components are, in particular, readily volatile nonionic surfactant components which, although no longer discharged into the environment with the waste gas in the process according to the invention, can nevertheless readily be added to the detergent as a whole by subsequent spraying onto absorbent tower powder which has been prepared in accordance with the invention.
The working conditions of the process according to the invention enable high temperatures to be used for the circulated steam phase in the drying step of the spray drying process. The working temperatures after superheating (reheating) are generally above 150.degree. C. and preferably at least about 200.degree. C. in the gas phase. Working temperatures of 250.degree. C. and higher can be particularly interesting and even temperatures of at least 300.degree. C. and more particularly in the range from 300.degree. to 380.degree. C. may be applied. In many cases, working temperatures in the range from about 270.degree. to 350.degree. C. in the steam phase are particularly suitable. All these temperature values relate to the temperature of the steam heated to optimal temperature which is delivered to the spray drying zone in co-current or countercurrent. The temperature of the steam falls in known manner during its contact with the wet or moist material. Considerations based largely on energy factors, including in particular the intended subsequent use of the steam to be removed from the circuit, determine the quantitative ratios between the quantity of water to be evaporated and the quantity of superheated steam delivered. Embodiments which provide only for a limited reduction in the steam temperature after leaving the spray drying zone to values in the range from about 190.degree. to 250.degree. C. are possible in this regard whereas, in other embodiments, the thermal energy of the steam can advantageously be further utilized to reduce the temperature of the steam to the vicinity of the condensation temperature under process conditions. More specifically, these details are determined inter alia by the design of the recycle process as a whole. Corresponding considerations apply to the use of superheated steam as the hot gas in an optional after-drying stage in the fluidized bed process. The figures mentioned above apply in this case also.
Basically, it may be said in respect of these considerations that the process is carried out in a closed-loop system with a steam circuit from which the water evaporated from the starting material is removed while the energy released in particular during the drying step is directly returned to the circuit. In one important embodiment, the steam removed is freed from entrained particles of material and put to another use as process steam, if desired after its pressure and temperature have been adapted to the required conditions. In another embodiment of the process according to the invention, the steam removed is at least partly condensed and freed from entrained particles of material. The liquid phase accumulating may be recycled to the drying process together with any of the useful material present therein. In this connection, it is possible, for example, to use vaporous fractions of the gas stream removed from the circuit to concentrate the aqueous liquid phase. The liquid recycled together with the useful material present therein may be directly delivered to the spray drying zone or may first be mixed with the fresh aqueous preparations and introduced in this form into the spray drying zone for drying.
In one particularly interesting embodiment of the invention, the heat of condensation of the steam removed from the circuit is recovered and utilized. By adopting suitable measures, it is even possible to recycle the small amounts of useful material which have left the primary steam circuit via the superheated steam removed therefrom. To this end, the following procedure, for example, may be adopted using the heat of condensation of the steam removed from the circuit:
Using the heat of condensation of the predominantly steam-containing mixed gas stream removed from the circuit, the steam condensate is concentrated in a preferably multiple-stage evaporation unit. The residual concentrate accumulating is returned to the primary process circuit. More particularly, this residual concentrate may be added to the slurry of useful material to be dried by superheated steam.
If necessary, the non-condensable residual gas phase, if any, accumulating during condensation of the superheated steam removed from the primary circuit (i.e. the non-condensable constituents, if any, present from the combustion gases used for heating, more particularly nitrogen and/or carbon dioxide where the steam is directly heated with hot waste gases) may be subjected to further working up during the condensation process. These gases may thus be freed from entrained residues of the material being dried. The additional working up may comprise such treatment steps as incineration or treatment in biofilters and/or in washing units. By this combination of substantially complete recycling of the particular steam-based streams and the reliable destruction of final residual traces in the comparatively limited quantities of non-condensable gases, the process according to the invention makes it possible for the first time in the industrial field with which the invention is concerned to recover useful materials and mixtures of useful materials from the field of detergents and cleaning products substantially or at least very largely free from waste air and free from polluted wastewater.
Irrespective of this and in addition to these considerations, the method according to the invention provides for appreciable savings of energy by comparison with conventional hot gas drying. Thus, through the circulation of steam at a comparatively high temperature level, the amount of heat to be introduced in the recycle process per kilogram of water to be evaporated is considerably reduced by comparison with conventional drying processes involving only a single passage of the hot drying gases. In addition to the absence of pollutants, therefore, the process according to the invention satisfies further requirements of modern technology for processes carried out on an industrial scale.
General particulars of useful materials for direct or indirect use in the production of wetting agents, detergents and/or cleaning products using the principles according to the invention are given in the following with reference to typical components of modern laundry detergents.
Suitable anionic surfactants are, for example, soaps of natural or synthetic, preferably saturated, fatty acids. Soap mixtures derived from natural fatty acids, for example coconut oil fatty acid, palm kernel oil fatty acid or tallow fatty acid, are particularly suitable. Soap mixtures of 50 to 100% saturated C.sub.12-18 fatty acid soaps and 0 to 50% oleic acid soap are preferred.
Other suitable synthetic anionic surfactants are those of the sulfonate and sulfate type. The process according to the invention can have particular significance for corresponding compounds of vegetable and/or animal origin.
Suitable surfactants of the sulfonate type are alkylbenzene sulfonates (C.sub.9-15 alkyl), olefin sulfonates, i.e. mixtures of alkene and hydroxyalkane sulfonates, and sulfonates of the type obtained, for example, from C.sub.12-18 monolefins with a terminal or internal double bond by sulfonation with gaseous sulfur trioxide and subsequent alkaline or acidic hydrolysis of the sulfonation products. Also suitable are the alkane sulfonates obtainable from C.sub.12-18 alkanes by sulfochlorination or sulfoxidation and subsequent hydrolysis or neutralization or by addition of bisulfites onto olefins and, more particularly, the esters of .alpha.-sulfofatty acids (ester sulfonates), for example the .alpha.-sulfonated methyl esters of hydrogenated coconut oil, palm kernel oil or tallow fatty acids.
Other important surfactant and emulsifier components in this regard are the so-called disalts which may be obtained by saponification of the above-mentioned .alpha.-sulfonated fatty acid methyl esters or by direct sulfonation of fatty acids, more particularly saturated C.sub.12-18 fatty acids. The process according to the invention thus makes it possible for the first time for surfactants of the type described here and in the following based on natural materials to be made available without difficulty on an industrial scale in the form of dry free-flowing concentrates which have virtually unlimited storage life and hence make a significant contribution to the universally desired replacement of ABS.
Suitable surfactants of the sulfate type are the sulfuric acid monoesters of primary alcohols of natural and synthetic origin, i.e. of fatty alcohols, for example coconut oil fatty alcohols, tallow fatty alcohols, oleyl alcohol, lauryl, myristyl, palmityl or stearyl alcohol, or the C.sub.10-20 oxoalcohols and those of secondary alcohols having the same chain length. Sulfuric acid monoesters of the alcohols of natural and/or synthetic origin ethoxylated in particular with 1 to 6 mol ethylene oxide are also suitable components. Such compounds as 2-methyl-branched C.sub.9-11 alcohols containing on average 3.5 mol ethylene oxide are mentioned as an example of synthetic alcohol. Sulfated fatty acid monoglycerides are also suitable.
The anionic surfactants may be present in the form of their sodium, potassium and ammonium salts and also as soluble salts of organic bases.
Suitable nonionic surfactants are adducts of 1 to 40 mol and preferably 2 to 20 mol ethylene oxide with 1 mol of an aliphatic compound essentially containing 10 to 20 carbon atoms from the group consisting of alcohols, carboxylic acids, fatty amines, carboxylic acid amides or alkane sulfonamides. Of particular importance are the adducts of 8 to 20 mol ethylene oxide with primary alcohols, for example with coconut oil or tallow fatty alcohols, with oleyl alcohol, with oxoalcohols or with secondary alcohols containing 8 to 18 and preferably 12 to 18 carbon atoms. In addition to the water-soluble nonionics, however, water-insoluble or substantially water-insoluble polyglycol ethers containing 2 to 7 ethylene glycol ether units in the molecule are also of interest, particularly when they are used together with water-soluble nonionic or anionic surfactants. It has already been pointed out that, in the process according to the invention, the tendency of nonionic surfactants such as these to be carried over can be taken into consideration by completely or partly applying components of this type to a correspondingly preformed tower powder on completion of spray drying. The same also applies in particular to nonionic surfactants liquid at room temperature.
Other suitable nonionic surfactants are alkyl glycosides corresponding to the general formula R--O--(G).sub.x, in which R is a primary linear or branched aliphatic radical containing 8 to 22 and preferably 12 to 18 carbon atoms, G stands for a glycose unit containing 5 or 6 carbon atoms and the degree of oligomerization x is between 1 and 10.
Suitable organic and inorganic builders are soluble and/or insoluble components showing a mildly acidic, neutral or alkaline reaction which are capable of precipitating or complexing calcium ions. Suitable and, in particular, ecologically safe builders are finely crystalline synthetic zeolites of the type already mentioned. Other builder components which, in particular, may be used together with the zeolites include (co)polymeric polycarboxylates, such as polyacrylates, polymethacrylates and, in particular, copolymers of acrylic acid with maleic acid, preferably those with 50% to 10% maleic acid. The molecular weight of the homopolymers is generally in the range from 1,000 to 100,000 while the molecular weight of the copolymers is in the range from 2,000 to 200,000 and preferably in the range from 50,000 to 120,000, based on free acid. A particularly preferred acrylic acid/maleic acid copolymer has a molecular weight of 50,000 to 100,000. Suitable, but less preferred compounds of this class are copolymers of acrylic acid or methacrylic acid with vinyl ethers, such as vinyl methyl ether, in which the acid makes up at least 50%. Other suitable builders are polyacetal carboxylic acids, for example of the type described in U.S. Pat. Nos. 4,144,226 and 4,146,495, and also polymeric acids which are obtained by polymerization of acrolein and subsequent disproportionation with alkalis and which are made up of acrylic acid units and vinyl alcohol units or acrolein units.
Suitable organic builders are, for example, polycarboxylic acids which are preferably used in the form of their sodium salts, such as citric acid and nitrilotriacetate (NTA), providing there are no ecological objections to their use.
In cases where a phosphate content can be tolerated, it is also possible to use phosphates, more particularly pentasodium triphosphate, and even pyrophosphates and orthophosphates which act primarily as precipitants for lime salts.
Suitable inorganic non-complexing salts are the bicarbonates, carbonates, borates or silicates of the alkali metals which are also known as "washing alkalis". Of the alkali metal silicates, sodium silicates with an Na.sub.2 O to SiO.sub.2 ratio of 1:1 to 1:3.5 are particularly suitable. From the remaining groups of typical detergent ingredients, components from the classes of redeposition inhibitors (soil suspending agents), neutral salts and fabric softeners are particularly suitable for use in the spray drying process according to the invention.
Suitable redeposition inhibitors are, for example, carboxymethyl cellulose, methyl cellulose, methyl hydroxy-ethyl cellulose and mixtures thereof. The above-mentioned sodium sulfate is cited as a typical example of a suitable representative of the neutral salts. Suitable softeners are, for example, swellable layer silicates of the montmorillonite type, for example bentonite.
As mentioned above, typical ingredients of detergents and cleaning products which are sensitive to high temperatures and/or liquid at room temperature, such as liquid nonionic surfactant components, bleaches based on per compounds, enzymes from the class of proteases, lipases and amylases or bacterial strains or fungi, stabilizers, fragrances, temperature-sensitive dyes and the like, are best mixed with the dry powders obtained beforehand.
Another example of embodiment of the invention is described in more detail in the following with reference to the accompanying drawings, wherein:

Process for the production of granules suitable as wetting agents, detergents and/or cleaning products


A method is disclosed for manufacturing a pharmaceutical tablet for oral administration, the tablet combining both immediate-release and prolonged-release modes of drug delivery and using an immediate-release drug that is either insoluble in water or only sparingly soluble and is present in a very small amount compared to the prolonged-release drug. The method involves the use of particles of the immediate-release drug that are equal to or less than 10 microns in diameter, applied as a layer or coating over a core of the prolonged-release drug, the layer or coating being either the drug particles themselves, applied as an aqueous suspension, or a solid mixture containing the drug in admixture with a material that disintegrates rapidly in gastric fluid. The result in both cases is a high degree of uniformity in the proportions of the immediate-release and prolonged-release drugs, uniformity that is otherwise difficult to achieve in view of the insolubility of the immediate-release drug and its relatively small amount compared to the prolonged-released drug.

1. Field of the Invention
This invention is in the field of pharmacology, and relates to drug dosage forms that are designed to deliver the drugs to human patients at particular rates.
2. Description of the Prior Art
Certain pharmacological therapies either require or benefit from the administration of drugs in a sequential manner. This can be done by a regimen in which the patient follows a prescribed time schedule, but because of patient non-compliance, scrupulous adherence to a schedule often requires the assistance of a medical professional. Even those therapies that involve only two dosages, such as an immediate but rapidly declining high-level dosage combined with a prolonged low-level or moderate-level dosage, either of the same drug or of two different drugs, can be a nuisance to the individual or troublesome to maintain if the individual is required to take separate unitary dosage forms. Certain pharmaceutical formulations have therefore been developed that combine both functions into a single dosage form. This simplifies the therapy and reduces or eliminates the chances of improper administration.
Many unitary dosage forms that have been proposed for combining immediate release with prolonged release do so by the placement of the drugs in different layers of a tablet or by placing one drug in a quickly-dissolving or quickly-dispersing coating over the surface of a slowly dissolving or swellable core that contains the other drug. With its high initial release concentration and rapid rate of decline, the immediate-release drug is often provided in a much lower amount than the prolonged-release drug. The immediate-release portion of the dosage form is therefore either a very thin layer or coating or a layer or coating with a very low concentration of the drug relative to the drug in the prolonged-released portion. It is common, for example, to design the dosage form such that the amount of drug intended for immediate release is {fraction (1/100)}th or less of the amount intended for prolonged release.
This large imbalance in the amounts of immediate-release and controlled-release drug creates problems in manufacturing, particularly in achieving uniformity from one tablet to the next. It is difficult to achieve uniform immediate-release coatings or layers of uniform drug content when the drug is so low in quantity or concentration. The problem is exacerbated when the drug in the immediate-release portion is one that has little or no solubility in water.
It has now been discovered that a dosage form that includes a core from which drug is released on a prolonged basis and a coating or layer from which drug is released on an immediate-release basis can be made in a manner that provides a high degree of uniformity in the immediate-release portion, even when the drug in the immediate-release portion is either insoluble or only sparingly soluble in water. This is achieved by limiting the drug particle diameter in the immediate-release coating or layer to 10 microns or less. The coating or layer is either the particles themselves, applied as an aqueous suspension, or a solid composition that contains the drug particles incorporated in a solid material that disintegrates rapidly in gastric fluid. Either mixture can be applied as a coating or layer over a core or coherent mass of the prolonged-release drug. When an aqueous suspension is used and applied as a coating, a suspending agent, binder, or both can be included to improve the procedure, and in either case, other excipients can be included to facilitate the manufacturing process.
Details on these and other features, advantages, and embodiments of the invention will be apparent from the description that follows.
The dosage forms of this invention are designed for oral ingestion, and the prolonged-release portion of the dosage form is one that delivers its drug to the digestive system continuously over a period of time of at least an hour and preferably several hours. The drug is retained in a matrix or supporting body of pharmaceutically inert solid, and the controlled delivery rate can be achieved by using a matrix that allows the gastric fluid to permeate the matrix and leach out the drug (i.e., allow the drug to diffuse out from the matrix as the drug slowly dissolves in the permeating fluid), or a matrix that slowly dissolves or erodes to expose the drug to the gastric fluid, or one that does both of these at once. The delivery rate is preferably slow enough that at least about 40% of the drug remains unreleased one hour after ingestion, more preferably at least about 60% and most preferably at least about 80%. In general, the drug will be substantially all released within about ten hours and preferably within about eight hours, and in most cases, the matrix supporting the drug will remain substantially intact until all of the drug is released. xe2x80x9cSubstantially intactxe2x80x9d in this sense means that the matrix retains its size and shape without dissolving or disintegrating into fragments.
The immediate-release portion of the dosage form is either a coating applied or deposited over the entire surface of a unitary prolonged-release core, or a single layer of a tablet constructed in two or more layers, one of the other layers of which is the prolonged-released portion. Immediate release of the drug from the immediate-release layer is achieved by any of various methods known in the art. One example is the use of a very thin layer or coating which by virtue of its thinness is quickly penetrated by gastric fluid allowing fast leaching of the drug. Another example is by incorporating the drug in a mixture that includes a supporting binder or other inert material that dissolves readily in gastric fluid, releasing the drug as the material dissolves. A third is the use of a supporting binder or other inert material that rapidly disintegrates upon contact with gastric fluid, with both the material and the drug quickly dispersing into the fluid as small particles. Examples of materials that rapidly disintegrate and disperse are lactose and microcrystalline cellulose. An example of a suspending agent and binder is hydroxypropyl methyl cellulose.
The dosage forms of this invention include those in which the same drug is used in both the immediate-release and the prolonged-release portions as well as those in which one drug is formulated for immediate release and another drug, different from the first, for prolonged release. This invention is particularly directed to dosage forms in which the immediate-release drug is at-most sparingly soluble in water, i.e., either sparingly soluble or insoluble in water, while the prolonged-release drug can be of any level of solubility. The immediate-release drug is of sufficiently low solubility that it remains a solid particle during the preparation of the dosage form when the dosage form is prepared without the use of organic solvents. The only dispersing medium, when one is used, is water or an aqueous solution that may contain other components. The term xe2x80x9cat most sparingly solublexe2x80x9d as used herein denotes a drug having a solubility in water at 37xc2x0 C. that is generally less than 2% by weight, preferably less than 0.5% by weight. The particle size of the drug as it is used in the practice of this invention is equal to or less than about 10 microns in diameter, preferably within the range of from about 0.3 micron to about 10 microns in diameter, and most preferably with the range of from about 1 micron to about 5 microns in diameter.
The immediate-release drug can thus be deposited as a suspension over a unitary core of the controlled-release drug, with deposition being achieved by coating techniques known in the pharmaceutical formulation art such as spraying, pan coating, and the like, or the drug can be combined with particles of a binding matrix and compressed over a preformed layer of the controlled-release drug to form a layered tablet. In either case, the immediate-release coating or layer separates relatively quickly from the remainder of the tablet after ingestion, leaving the remainder intact. The weight ratio of the immediate-release drug to the prolonged-release drug is about 0.01:1 or less, preferably from about 0.001:1 to about 0.01:1.
In certain preferred embodiments of the invention, the supporting matrix in controlled-release portion of the tablet is a material that swells upon contact with gastric fluid to a size that is large enough to promote retention in the stomach while the subject is in the digestive state, which is also referred to as the postprandial or xe2x80x9cfedxe2x80x9d mode. This is one of two modes of activity of the stomach that differ by their distinctive patterns of gastroduodenal motor activity. The xe2x80x9cfedxe2x80x9d mode is induced by food ingestion and begins with a rapid and profound change in the motor pattern of the upper gastrointestinal (GI) tract. The change consists of a reduction in the amplitude of the contractions that the stomach undergoes and a reduction in the pyloric opening to a partially closed state. The result is a sieving process that allows liquids and small particles to pass through the partially open pylorus while indigestible particles that are larger than the pylorus are retropelled and retained in the stomach. This process causes the stomach to retain particles that are greater than about 1 cm in size for about 4 to 6 hours. The controlled-release matrix in these embodiments of the invention is therefore selected as one that swells to a size large enough to be retropelled and thereby retained in the stomach, causing the prolonged release of the drug to occur in the stomach rather than in the intestines.
Disclosures of oral dosage forms that swell to sizes that will prolong the residence time in the stomach are found in U.S. Pat. No. 5,007,790 (xe2x80x9cSustained-Release Oral Drug Dosage Form;xe2x80x9d Shell, inventor; Apr. 16, 1991), U.S. Pat. No. 5,582,837 (xe2x80x9cAlkyl-Substituted Cellulose-Based Sustained-Release Oral Drug Dosage Forms;xe2x80x9d Shell, inventor; Dec. 10, 1996): U.S. Pat. No. 5,972,389 (xe2x80x9cGastric-Retentive Oral Drug Dosage Forms for the Controlled Release of Sparingly Soluble Drugs and Insoluble Matter;xe2x80x9d Shell et al., inventors; Oct. 26, 1999); International (PCT) Patent Application WO 98/55107 (xe2x80x9cGastric-Retentive Oral Drug Dosage Forms for Controlled Release of Highly Soluble Drugs;xe2x80x9d Shell et al., inventors; publication date Dec. 10, 1998); United States Patent Application Publication No. US 2001/0018707 A1 (xe2x80x9cExtending the Duration of Drug Release Within the Stomach During the Fed Mode;xe2x80x9d Shell et al., inventors, publication date Aug. 30, 2001); and International (PCT) Patent Application WO 96/26718 (xe2x80x9cControlled Release Tablet;xe2x80x9d Kim, inventor: publication date Sep. 6, 1996). Each of the documents cited in this paragraph is incorporated herein in its entirety.
In general, swellable matrices contain binders that are water-swellable polymers, and suitable polymers are those that are non-toxic, that swell in a dimensionally unrestricted manner upon imbibition of water, and that release the drug gradually over time. Examples of polymers meeting this description are:
cellulose polymers and their derivatives including, but not limited to, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropylmethyl cellulose, carboxymethylcellulose, and microcrystalline cellulose
polysaccharides and their derivatives
polyalkylene oxides
polyethylene glycols
chitosan
poly(vinyl alcohol)
xanthan gum
maleic anhydride copolymers
poly(vinyl pyrrolidone)
starch and starch-based polymers
maltodextrins
poly (2-ethyl-2-oxazoline)
poly(ethyleneimine)
polyurethane hydrogels
crosslinked polyacrylic acids and their derivatives
Further examples are copolymers of the polymers listed above, including block copolymers and graft polymers. Specific examples of copolymers are PLURONIC(copyright) and TECTONIC(copyright), which are polyethylene oxide-polypropylene oxide block copolymers available from BASF Corporation, Chemicals Div., Wyandotte, Mich., USA. Further examples are hydrolyzed starch polyacrylonitrile graft copolymers, commonly known as xe2x80x9cSuper Slurperxe2x80x9d and available from Illinois Corn Growers Association, Bloomington, Ill., USA.
Particularly preferred polymers are poly(ethylene oxide), hydroxypropyl methyl cellulose, and combinations of poly(ethylene oxide) and hydroxypropyl methyl cellulose.
As indicated above, the dosage forms of the present invention find utility when administered to subjects who are either in the fed mode or the fasting mode. Administration during the fed mode is preferred, since the narrowing of the pyloric opening that occurs in the fed mode serves as a further means of promoting gastric retention by retaining a broader range of smaller dosage form sizes.
The fed mode is normally induced by food ingestion, but can also be induced pharmacologically by the administration of pharmacological agents that have an effect in this regard that is the same or similar to that of a meal. These fed-mode inducing agents may be administered separately or they may be included in the dosage form as an ingredient dispersed in the dosage form or in an outer immediate-release coating. Examples of pharmacological fed-mode inducing agents are disclosed in co-pending U.S. patent application Ser. No. 09/432,881, filed Nov. 2, 1999, entitled xe2x80x9cPharmacological Inducement of the Fed Mode for Enhanced Drug Administration to the Stomach,xe2x80x9d inventors Markey, Shell, and Berner, the contents of which are incorporated herein by reference.
The size, shape, and dimensions of the tablet are not critical to the invention, provided that in embodiments where a swellable matrix is used, the tablet is sufficiently sized that upon swelling it reaches the dimensions that will be retained in the stomach during the fed mode. The tablet may be circular or elongated. An elongated tablet may be 18 to 22 mm in length, 6.5 to 10 mm in width, and 6.2 to 7.5 mm in height. A specific example is one that is 20 mm in length, 6.7 mm in width, and 6.4 mm in height. Again, these are merely examples; the shapes and sizes can be varied considerably.
Tablets in accordance with this invention can be prepared by conventional mixing, comminution, and tabletting techniques that are well known in the pharmaceutical formulations industry. The controlled-release portion can for example be fabricated by direct compression by punches and dies fitted to a rotary tabletting press, ejection or compression molding, granulation followed by compression, or forming a paste and extruding the paste into a mold or cutting the extrudate into short lengths. The immediate-release portion can be applied as a coating over the controlled-release portion by spraying, dipping, or pan-coating, or as an additional layer by tabletting or compression in the same manner as the controlled-release portion.
When tablets are made by direct compression, the addition of lubricants may be helpful and is sometimes important to promote powder flow and to prevent capping of the tablet (the breaking off of a portion of the tablet) when the pressure is relieved. Useful lubricants are magnesium stearate (in a concentration of from 0.25% to 3% by weight, preferably about 1% or less by weight, in the powder mix), and hydrogenated vegetable oil (preferably hydrogenated and refined triglycerides of stearic and palmitic acids at about 1% to 5% by weight, most preferably about 2% by weight). Additional excipients may be added to enhance powder flowability, tablet hardness, and tablet friability and to reduce adherence to the die wall.
The drug that is contained in the controlled release portion of the tablet may be any chemical compound, complex or composition that is suitable for oral administration and that has a beneficial biological effect, preferably a therapeutic effect in the treatment of a disease or an abnormal physiological condition. The drug can be either a high-solubility drug or a sparingly soluble or insoluble drug, all referring to solubility in water or aqueous media. Examples of high solubility drugs are metformin hydrochloride, vancomycin hydrochloride, captopril, lisinopril, erythromycin lactobionate, ranitidine hydrochloride, sertraline hydrochloride, ticlopidine hydrochloride, baclofen, amoxicillin, cefuroxime axetil, cefaclor, clindamycin, levodopa, doxifluridine, tramadol, fluoxitine hydrochloride, bupropion, potassium chloride, and esters of ampicillin. Examples low solubility drugs are saguinavir, ritonavir, nelfinavir, thiamphenicol, ciprofloxacin, calcium carbonate, clarithromycin, azithromycin, ceftazidime, acyclovir, ganciclovir, cyclosporin, digoxin, paclitaxel, iron salts, topiramate, ketoconazole, and sulfonylureas such as glimepiride, glypuride, and glipizide. Other drugs suitable for use will be apparent to those skilled in the art. This invention is of particular interest for antibiotics and angiotensin converting inhibitors, particularly lisinopril, enalapril, captopril, and benazepril. A particularly preferred group of drugs is lisinopril, acyclovir, metformin hydrochloride, baclofen, ciprofloxacin, furosemide, cyclosporin, sertraline hydrochloride, and calcium carbonate. The drug that is contained in the immediate-release portion of the tablet is a sparingly soluble or insoluble drug, such as those listed above. Combinations of particular interest are metformin hydrochloride in the controlled-released portion and a sulfonylurea such as glimerpiride, glyburide, or glipizide in the immediate-release portion. Metformin hydrochloride and glimepiride are particularly preferred.

Manufacture of oral dosage forms delivering both immediate-release and sustained-release drugs